1. Field of the Invention
The present invention relates to a safety device for industrial vehicles such as fork trucks and front end loaders. More specifically, the invention provides a safety control for a loader such as a fork lift truck which precludes possibly hazardous operation of the vehicle unless the operator and the operator's vulnerable appendages are fully within the vehicle.
2. Description of the Prior Art
Industrial vehicles typically include a cab portion having a control station such as an operator's seat from which the machine is operated and from which the operator can initiate and control various functions, for example load manipulation, vehicle movement, and the like. Various means have been proposed either to restrain the operator safely within the cab or to prevent operation of the vehicle unless the operator is properly in position.
U.S. Pat. No. 3,507,350--Boyajian relates to a safety control for a vehicle wherein the vehicle is prevented from movement when the operator leaves a seat in the cab. A limit switch sensitive to the weight of the operator on the seat is connected in the electric motor drive control circuit as an interlock. Similar controls are known in which interlock switch contacts are connected to sense closure of operator seat belts or other elements bearing downwardly against the operator, in each case permitting operation only when the operator is in the seat.
The foregoing controls are electric and concern electrically drivin devices. U.S. Pat. No. 3,983,347--Brenzen discloses an automatic kill switch assembly for internal combustion engines which stops the engine of a vehicle when the driver leaves the vehicle as sensed, for example, by release of hand pressure on the throttle control. The kill switch can be connected into the ignition system.
U.S. Pat. No. 4,172,980--Hsieh et al discloses a device for controlling a propulsion system of a lift truck by interrupting power flow in response to any of a plurality of non-operating conditions.
The foregoing prior art discloses various means designed to prevent intentional or unintentional movement of the vehicle when the operator is not in the safe position as sensed by certain means responsive to typical proper operation. The disclosures of these references are incorporated herein for the particulars of their circuit connections and interlocks. None of the controls of the references, however, senses a very common dangerous condition which results when an operator is in the correct position for proper operation, but allows either a body part or other means to extend out of the protected cab area into areas alongside the cab. None of the references teach interlocks for sensing dangerous conditions in this area outside the cab, and halting operations if the operator's foot or leg or the like protrudes from the cab while the operator is in proper position in the cab.
Many injuries have been sustained when loaders such as fork lift trucks are operated while the operator's leg or foot is left outside of the truck's cab. Known seat restraints merely keep the operator's torso in the seat. These devices do not restrain the operator's arms, feet or legs within the truck's cab and thus do not prevent crushing injury which occurs if the cab brushes past a wall, crate or other object or barrier nearby, or closely passes another vehicle, when the arm, leg or foot is outside of the cab. Such injuries are common.
Operators must often move in and out of the cab to accomplish various functions. Passage into and out of the cab must be kept clear to avoid impeding the operator. Unfortunately, the need for a clear passage and the need to frequently move in and out encourage the operator to use one foot for foot controls and to leave the other foot outside. Even if an operator is willing to keep both feet in the cab, or if an interlock is designed (e.g. with floor switches for each foot) to require presence of both feet for operation, a danger remains that protruding items such as other operator appendages or the operator's jacket, items such as broomsticks or the like in the cab, could contact or become entangled on items outside. In that event, the entangled item can cause the operator to be struck or pulled from the vehicle, with resultant injuries. When an operator realizes that a foot will be crushed or other injury sustained, it is often too late to retract the protruding foot or other item. In any event, operators of vehicles such as fork trucks typically concentrate so entirely on their loads that they frequently do not forsee the impending danger.
According to the invention a sensor is arranged in a danger zone outside the cab rather than in the zone of proper operation. Therefore, even if the driver is in place, with weight on the seat and hands on the controls, etc., any protruding item extending into the area to be traversed by passing obstructions will activate an alarm and/or an operator-stopping interlock. Unnecessary alarms and interlocks are prevented by placing the sensor field immediately adjacent the entryway to the cab, preferably defining a detection zone extending across the entryway or just below the entryway with a light beam traversing the entryway or running immediately adjacent the surface of the vehicle just below the entryway opeining. Protruding items such as the operator's foot become disposed in the sensed field, for example breaking the light beam and changing the state of a photocell, whereupon an alarm and/or interlock is activated.